This invention relates to a system that allows authorized vehicles to remotely control traffic signals, and more specifically, to an optical signal emitter assembly for use in such a system, wherein an optical signal emitter assembly attached to an approaching authorized vehicle transmits a stream of light pulses to a detector mounted near a traffic intersection causing a preemption request to be issued to a traffic signal controller.
Traffic signals have long been used to regulate the flow of traffic at intersections. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed.
Emergency vehicles, such as police cars, fire trucks and ambulances, generally have the right to cross an intersection against a traffic signal. Emergency vehicles have typically depended on horns, sirens and flashing lights to alert other drivers approaching the intersection that an emergency vehicle intends to cross the intersection. However, due to hearing impairment, air conditioning, audio systems and other distractions, often the driver of a vehicle approaching an intersection will not be aware of a warning originating from an approaching emergency vehicle. This can create a dangerous situation when an emergency vehicle seeks to cross an intersection against a traffic signal and the driver of another vehicle approaching the intersection is not aware of the warning being transmitted by the emergency vehicle.
This problem was first successfully addressed in U.S. Pat. No. 3,550,078 (Long), which is assigned to the same assignee as the present application. The Long patent discloses an emergency vehicle with an optical emitter, a plurality of detectors mounted along an intersection with each detector looking down an approach to the intersection, a plurality of signal processing circuits located in the detectors which produce a signal representative of the distance of the approaching emergency vehicle, and a phase selector which processes the signal from the processing circuits and can issue a request to a traffic signal controller to preempt a normal traffic signal sequence and provide green lights to the approaching emergency vehicle.
The Long patent discloses that as an emergency vehicle approaches an intersection, it emits a stream of light pulses at a predetermined rate, such as 10 pulses per second, and with each pulse having a duration of several microseconds. A detector receives the light pulses emitted by the approaching emergency vehicle. An output of the detector is processed by the phase selector, which then issues a request to a traffic signal controller to change to or hold green the traffic signal lights that control the emergency vehicle's approach to the intersection.